It’s a secret that has remained hidden underneath Liverpool for centuries – a mysterious network of tunnels right below the city's streets.

Built around 200 years ago, they stretch on for miles creating a vast subterranean labyrinth of twisting routes and caverns. Yet little is known about the forgotten tunnels, which were only rediscovered in 2001.

They were created by the rather eccentric Joseph Williamson, a successful tobacco merchant, who was incredibly secretive about the build throughout his lifetime.

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The Williamson Tunnels: The network of chambers underneath the city of Liverpool have been rediscovered after 200 years

The vast caverns were built by eccentric philanthropist Joseph Williamson, although his purpose remains unclear

Yet little is known about the forgotten tunnels, which were only rediscovered in 2001 by a local history group

The tunnels stretch on for miles, creating a vast subterranean labyrinth of twisting routes and caverns

Excavators explore the secret tunnels underneath the busy city centre streets in Liverpool

Historians are hopeful that one day they will discover secret documents belonging to Wiliamson that explain the tunnels once and for all

With no records from Williamson's time to offer an explanation, the network's true purpose or even how far it spans is still unknown - leaving experts baffled, reports BBC Future

Some claim that the successful businessman and his wife had been part of an apocalyptic cult that had predicted the end of the world. The tunnels would provide shelter after the end of days.

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He was certainly reported to be very secretive about his work, only allowing certain people to see inside the hidden passageways, in which gothic, chapel-like features can be seen.

They were created by the rather eccentric Joseph Williamson, a successful tobacco merchant, who was incredibly secretive about the build throughout his lifetime

Others say they were a ploy to keep men in the area - which had high levels of unemployment following the Napoleonic wars - in work.

He was well known for his philanthropy in the area, which is perhaps how he earned the nickname 'The King of Edge Hill', while there are stories of workers being told to perform apparently pointless duties, such as instructing a man to move a pile of rocks only to get him to move them back again.

There is also evidence of tunnels being built and immediately bricked up again, and arches built that lead nowhere.

This may support the suggestion of a purely philanthropic exercise but may also hint at attempts to keep the true size and certain parts of the chambers secret.

The cavern system even has an entrance in the basement of his former home, leading to suggestions he used them for smuggling or other secret operations.

What is apparent is that Williamson was obsessed.

After the death of his wife Elizabeth, in 1822, aged 56, he is said to have sought solace in his labyrinth - with reports that he was barely seen above ground again.

The tunneling finally stopped immediately after his death aged 70 in May 1840.

The passages were later blocked up and forgotten about for hundreds of years until a local history group rediscovered them in 2001.

'A lot of people knew about the tunnels, but that was as far as it went – they just knew about them or heard about them,' Les Coe, an early member of the Friends of Williamson Tunnels (FoWT) told the BBC.

'It was just left at that. But we decided to look for them.'

With the help of a digger, the group finally broke into the tunnels in Edge Hill, Liverpool and have been excavating ever since.

But it's been a challenge.

Aside from the difficulty of removing material from the deep caverns and multiple level cellar systems, the effort relies on a team of volunteers, most of whom are retirees, who work twice a week.

Experts cannot agree on why Williamson created the tunnels, with some claiming it was a redevelopment attempt decades ahead of its time

Work is now underway to excavate the tunnels which were dug in the early 19th century

With no records from Williamson's time to offer an explanation, the network's true purpose or even how far it spans is still unknown - leaving experts baffled

Some claim that the successful businessman and his wife had been part of an apocalyptic cult that had predicted the end of the world

Some historians believed that Willamson thought the tunnel network would be used as a shelter for the end of days

Others say they were a ploy to keep men in the area - which had high levels of unemployment following the Napoleonic wars - in work

Flats and homes above ground mean that permission to grant a new section of tunnel is sometimes refused over safety fears.

Over the last 14 years, the group have raised more than 120 skips of rubble but admit they have no idea how far the vast labyrinth stretches on for.

Amongst the rubbish, is a treasure trove of local history, such as poison bottles, clay pipes, oyster shells and ceramics from Liverpool's Royal Infirmary, offering an unusual insight into Liverpool life.

However their next target is a blocked up tunnel which they believe could lead to a brand new system of undiscovered chambers.

The Williamson Tunnels Heritage Centre has now been opened so visitors can learn about the mysterious tunnels

There is also evidence of tunnels being built and immediately bricked up again, and arches built that lead nowhere

Excavations have been underway since the tunnels were first discovered in 2001 and are still ongoing

During the dig, excavators have found a whole treasure trove of historical items giving an insight to 19th century Liverpol

They include ceramics from a local hospital, glasses, bottles which held everything from poison to beer

The entrance to the eccentric Williamson's network of tunnels - which has left experts baffled to its purpose

Locals have now come up with their own theory behind the mysterious Williamson tunnels.

Dave Bridson, a local historian and manager at the Williamson Tunnels heritage centre in Liverpool, denied cultist theories as 'total guff.'

'He was quite a devout Christian and a Church of England member,' he told the BBC.

Instead, he believes that Williamson could have been decades ahead of time in redeveloping an area.

He believes that pits in the ground already existed - rendering the land worthless as it would support little weight.

Williamson then decided to construct arches over them, a popular method of construction in the 1800s, which would have allowed the area to be developed. Mr Bridson claimed filling in the land using 19th century methods would have taken too long.

However, the historian is hopeful that one day they will discover secret documents belonging to Wiliamson that explain the tunnels once and for all.

'Part of me clings on to that hope,' he said.

Until then, the mystery must continue.

The side of the excavated tunnel has been put on display at the heritage centre in Liverpool

Locals have now come up with their own theory behind the mysterious Williamson tunnels

Dave Bridson, a local historian and manager at the Williamson Tunnels heritage centre in Liverpool, denied cultist theories as 'total guff'

Some believe that pits in the ground already existed - rendering the land worthless as it would support little weight, while Williamson built the arches to support the ground and allow development